Tephra layers within marine sediments provide information on past explosive eruptions, which is especially important in the case of remote island arcs where data on proximal pyroclastic deposits can be scarce. Three Alaska-Aleutian tephras (labeled Br2, SR2, and SR4) were found in the late Pleistocene-Holocene sediments of the Bering Sea (north Pacific). We fingerprint glass from these tephras with the help of single-shard electron microprobe and LA-ICP-MS analyses and provide microprobe data on minerals from two of these tephras. The large compositional variability of the Alaska-Aleutian volcanoes permits the use of ratios of highly incompatible trace elements (Ba/Nb, Th/Nb, Th/La, La/Nb) for identification of distal tephra sources by comparison of these ratios in tephra glass and proximal bulk rock analyses. This method, along with mapped tephra dispersal, has allowed us to link tephras under study to Aniakchak, Semisopochnoi, and Okmok volcanoes, respectively. Our results indicate that tephra Br2 was derived from the ~ 3.6 ka Aniakchak II caldera-forming eruption (Alaska, USA). This is the first ever finding of the Aniakchak II tephra in Bering Sea sediments, which permits enlargement of its tephra volume and eruption magnitude to ~ 100 km 3 and 6.8, respectively. Tephra SR2, dated at ~ 12.2 ka, is likely associated with a post-glacial caldera on the Semisopochnoi Island, Aleutians (USA). Tephra SR4 (dated at ~ 64.5 ka), likely was derived from an earlier undocumented eruption from Okmok volcano (Aleutians). All three regionally spread tephra layers are valuable isochrones, which can be used for correlating and dating of Bering Sea sediments.

We used piston cores recovered in the western Bering Sea to reconstruct millennial-scale changes in marine productivity and terrigenous matter supply over the past ~180 kyr. Based on a geochemical multi-proxy approach, our results indicate closely interacting processes controlling marine productivity and terrigenous matter supply comparable to the situation in the Okhotsk Sea. Overall, terrigenous inputs were high, whereas export production was low. Minor increases in marine productivity occurred during intervals of Marine Isotope Stage 5 and interstadials, but pronounced maxima were recorded during interglacials and Termination I. The terrigenous material is suggested to be derived from continental sources on the eastern Bering Sea shelf and to be subsequently transported via sea ice, which is likely to drive changes in surface productivity, terrigenous inputs, and upper-ocean stratification. From our results we propose glacial, deglacial, and interglacial scenarios for environmental change in the Bering Sea. These changes seem to be primarily controlled by insolation and sea-level forcing which affect the strength of atmospheric pressure systems and sea-ice growth. The opening history of the Bering Strait is considered to have had an additional impact. High-resolution core logging data (color b*, XRF scans) strongly correspond to the Dansgaard–Oeschger climate variability registered in the NGRIP ice core and support an atmospheric coupling mechanism of Northern Hemisphere climates.

Bottom sediments from the central zone of the Sea of Okhotsk were preliminarily dated. The petromagnetic parameters of two groups of samples formed at cold and warm climatic stages were studied. Warm oxygen isotopic stages and substages were characterized by the coexistence of pseudo-single-domain allogenic magnetite and predominant magnetite and greigite (pyrrhotite) grains subject to biologic control. At cold stages, sediments containing a mixture of pseudo-single-domain and multidomain terrigenous magnetite particles accumulated. The petromagnetic curves agree with the normalized standard oxygen isotopic curve over the last 350 kyr of the column section.

Based on fundamental laws of physicochemical mechanics of disperse structures, a magnetorheological model of lithogenetic structures in open (far from land) regions of the Pacific Ocean is constructed. Special attention is given to the magnetization mechanism of bottom sediments below the water-seafloor interface. This process is most active in the so-called Tucker-Khramov zone, where strength properties of a suspension are either unobservable or weak. A quantitative model describing both the filtering (smoothing) of a geomagnetic signal and its time lag in the rheological Tucker-Khramov zone is proposed for sedimentary rocks of various water contents. In the lower part of the zone, the sediment is a thixotropic solidifying structure in which the spatial orientation of magnetic dipoles is fixed due to an increase in the strength properties of the soil.

P4 - 03 GEOMAGNETISM PALAEOMAGNETISM & MAGNETOSTRATIGRAPHY MAGNETOSTRATIGRAPHY OF THE UPPER SEDIMENTARY STRATUM NEAR HOLE DSDP-159 (PACIFIC OCEAN) M.I. Malakhov G.Yu. Malakhova E.I. Vedernikov North-East Interdiscipinary Scientific Research Institute Russian Academy of Science Madagan Russia Formation of geological bodies with high concentration of mineral components in the deep-water sedimentologic genesis depends both on sources of these components and mostly on conditions of their concentration during sedimentation. With the wide variety of environments in which formation of iron-manganese nodules (IMN) is possible the following fact was established: nodule ore-formation is confined to pelagic ocean regions where it is not suppressed by

The attachment is easily operated, gives readings to an accuracy of the order 0.1 mm, and is of simple construction.